1. Field of the Invention
This invention relates to surgical fasteners used to join body tissue and more particularly to surgical fasteners which are composed of a material and configured to work their way out of body tissue after a limited period of time.
2. Background of the Art
Surgical fasteners have been used in operating procedures to eliminate the need for suturing, which is both time consuming and inconvenient. In many applications the surgeon can use a stapler apparatus, i.e., a fastener implanting device loaded with one or more surgical fasteners, to accomplish in a few seconds what would have taken many minutes to perform by suturing. This reduction in operating time reduces blood loss and trauma to the patient.
Surgical fasteners have been in the form of metal staples which are bent by the delivery apparatus to hook together body tissue. Such staples are typically made from biocompatible metals such as stainless steel alloys or titanium.
Two-part fasteners are also known, as illustrated in U.S. Pat. No. 4,506,670, in which a barbed fastener is used in conjunction with a retaining piece to hold the fastener in place.
Typically, the two-part fastener comprises a backspan and two barbed prongs which are engaged and locked into a separate retainer piece. In use, the fastener is pressed into the body tissue so that the barbs penetrate the tissue and emerge from the other side where they are then locked into the retainer piece. The retainers prevent the fastener from working loose from the tissue. The two piece fasteners cannot be unlocked and are not easily removable. For this reason, they must be made of a bioabsorbable material.
Possible materials include polymers and copolymers of glycolic acid (i.e. hydroxyacetic acid), the cyclic dimer of glycolic acid ("glycolide"), lactic acid, the cyclic dimer of lactic acid ("lactide") and related monomers. Polymers and copolymers of the foregoing kind and absorbable surgical devices made therefrom are well known. See, e.g., U.S. Pat. Nos. 2,668,162; 2,703,316; 2,758,987; 3,225,766; 3,297,033; 3,422,181; 3,531,561; 3,565,869; 3,620,218; 3,626,948; 3,636,956; 3,736,646; 3,772,420; 3,773,919; 3,792,010; 3,797,499; 3,839,297; 3,867,190; 3,878,284; 3,982,543; 4,060,089; 4,137,921; 4,157,437; 4,234,775; 4,237,920; 4,300,565; and 4,523,591; U.K. Patent No. 779,291; D. K. Gilding et al., "Biodegradable polymers for use in surgery--polyglycolic/poly(lactic acid) homo- and co-polymers: 1, Polymer, Volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.) Biocompatibility of Clinical Implant Materials, Vol. II, ch. 9: "Biodegradable Polymers" (1981).
U.S. Pat. No. 4,667,674 to Korthoff et al discloses a two part surgical fastener comprising a fastener member and a retainer member. The fastener member has a base, and a pair of prongs extending perpendicularly from the base. The prongs are spaced inward from the respective ends of the base in order to prevent splaying of the prongs, and to improve hemostasis.
The two piece fasteners require the staple delivery apparatus to have access to both sides of the tissue. Usually, such devices have a U-shaped member into which tissue is inserted. The stapler apparatus has a fastener holder and an anvil which are pivotally connected at one end, and mounted on the legs of the U-shaped support structure. See, for example, U.S. Pat. No. 4,402,445 to Green which discloses a surgical fastener and means for applying same. In a surgical operation, the tissue to be joined is positioned between the fastener holder and the anvil, which contains the fastener retainers. The fasteners are ejected from the holder into the tissue, and the prongs are locked into the retainers.
In some applications, however, it is not possible to have access to body tissue from two opposite directions. For example, in skin grafting applications one can only apply fasteners from a stapler positioned above the skin.
The prior art includes many examples of surgical staplers which do not enclose the body tissue between an anvil and fastener holder. For example, surgical staplers such as those described in U.S. Pat. No. 3,643,851 and U.S. Pat. No. 4,618,086 approach the skin from one direction. However, they require the use of staples which are malleable enough to be crimped by an anvil so that the prongs hook into the tissue. Typically, such staples are made of metal and are not bioabsorbable. They must be removed by another device such as a stapler extractor which is not only time consuming but can cause discomfort and pain to the patient. The discomfort and pain in removal of the staples are especially acute when the fasteners are used in skin grafting a burn victim. The sensitivity of the burn patient's skin cannot be understated; any contact with their skin causes distress, let alone removal of fasteners inserted through the skin and embedded in underlying body tissue.
Single piece barbed fasteners made from bioabsorbable material are known. U.S. Pat. No. 4,635,637 discloses a fastener having a base member and two substantially parallel shafts upstanding from the base member, the ends of the shafts each having a barb. The barbed fastener is disclosed as being useful in the repair of meniscal tissue. Pending patent application Ser. Nos. 372,025 filed Jun. 27, 1989, now issued U.S. Pat. No. 5,089,009 and 314,368 filed Feb. 22, 1989, now issued U.S. Pat. No. 4,994,073 also disclose bioabsorbable fasteners having barbs. If these fasteners are removed, then the patient will suffer from the same distress as described above with respect to non-bioabsorbable staples.
The prior art fasteners discussed above were designed with the intention that significant vertical support was required. Thus, outwardly extending barbs were provided on their prongs to ensure that they remained embedded in the body tissue for a sufficiently long period of time. However, such barbed fasteners remained in the tissue for a longer time than was necessary. The need therefore exists for a fastener which remains embedded in the tissue only for a sufficient period of time to allow healing to commence but avoids the discomfort and pain associated with the removal of prior fasteners.